During the last 3 years, Dr. Schoen and the Cardiac Pathology Laboratory have fruitfully collaborated with several of the individual investigators (Drs. Christine and Jonathan Seidman, Dr. Eva Neer) by interpreting myocardial pathology in experimental mutant hearts and clinical specimens of cardiomyopathy. In this SCOR, we propose the following specific aims: 1) provide expertise, techniques and facilities for morphological evaluation of cardiovascular specimens pertaining to the individual projects, 2) interpret morphological phenotypes in experiment mutant hearts and clinical specimens, and correlate these results in the context of substantial previous clinical and laboratory experience in the pathology of human myocardial disease, and 3) consult on experimental design and development of new techniques or adaptations of existing technology to the specific requirements of the individual projects. Specific services to be provided by the Core include: evaluation of gross specimens; preparation of slides for light microscopic histologic assessment; interpretation of slides of cardiovascular tissues by an experienced cardiovascular pathologist; correlate morphologic findings with those of human myocardial disease; preparation of tissues by an experienced cardiovascular pathologist; correlate morphologic findings with those of human myocardial disease; preparation of tissues for ultrastructural examination and their interpretation by transmission electron microscopy and scanning electron microscopy as needed; morphometric assessment at the light microscopic or ultrastructural level; immunocytochemistry at the light and electron microscopic level, localization by in-situ hybridization of mRNA/DNA in tissues; and consultation on experimental design. This Core will also collaborate with the investigators of the Isolated Myocyte and Whole Heart Physiology Core to provide periodic histology on cultured myocytes and assess tissues from hearts studied in physiologic experimentations. This will allow additional evidence of consistency and quality of cell and organ isolation and preparation and thereby improve overall data interpretation.